Sugar (usually pre-pulverised), chocolate liquor and whole milk powder are first mixed to form a paste that can be passed through a five-roll refiner. The paste is ground to an average particle size, which for regular commercial chocolate is about 10-15 ^m.
This paste is filled into a machine known as a conche, within which there is dry mixing and aeration on a massive scale. During the conching process, which can take between 6 and 72 h, the moisture and volatile acids are evaporated which results in a reduction of the viscosity of the chocolate. For milk chocolate, conching is performed at 50-65°C, but for dark chocolate it is in the range 60-90°C.
Due to the high shearing forces for long periods in the conching process, major changes occur in the texture. The finished chocolate is more cohesive, less crumbly when set, and the taste is much more mellow and less harsh and bitter. The loss of acetic acid ensures a reduction in acid taste. Chocolate receiving high-shearing action and, therefore, better aeration, shows a reduction in astringency, which would suggest that further oxidation of polyphenols is occurring.
During lengthy shearing, there is a better distribution of fat over the dry particles, especially the highly flavoured 'spikey' particles. This may result in a smoother, less bitter astringent taste in the finished chocolate.
The final step in the conching process is the addition of lecithin to reduce the viscosity of chocolate to a workable rheological mass.
The chocolate is now ready for use in either a coating or moulding operation.
Cocoa butter has five distinct polymorphs and, before it can be used in coating or moulding, it must be put through a cooling, mixing regime to achieve the correct stable form V polymorph. This process is called tempering. There are literally dozens of ways to achieve the correct stable cocoa butter crystallisation.
Tempering involves first cooling the chocolate with agitation, taking the temperature from 45-50°C to approximately 27-28°C. At this point, the chocolate is quite viscous and will contain the unstable form IV polymorph. The temperature is then raised to a working temperature of between 29 °C and 32.5°C, which will vary depending on the source of cocoa butter and the presence of anhydrous dairy butter fat. After coating and moulding, the chocolate must be carefully cooled to avoid the re-introduction of form IV crystals. The chocolate is now ready for packing and is preferably held at a constant 18°C during the distribution cycle.
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